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Underfill Rework

Rework of Underfilled Device

Underfills  protect the active surface of the die of flip chips, BGA ad CSP package types while improving their reliability by distributing stress away from the solder interconnects. This increases the performance of products in meeting drop, shock and bend criteria. Newer underfills are specifically designed to minimize the need to scrap entire boards with high cost devices bonded on them because testing has determined that a device is defective. However, the ability of these devices to be reworked once they have been underfilled, is challenging and time-consuming.

The goal of this type of rework project is to remove the underfilled device replacing it with a good die. The removal of this material can be accomplished either with mechanical grinding or through high temperature vacuum extraction or hand toolsdepending on the modulus of elasticity of the underfill.

The rework process begins with the even heating of the substrate to a temperature above the softening  point of the underfill. The package is mechanically gripped or pried with enough torque to break the fillet’s adhesions to the board. The chip undergoing rework is then heated above the solder  reflow temperature to melt the solder connections and break down the underfill. The device is then removed from the PCB.  Residual solder and underfill are cleaned off the substrate.  Cleanup after chip removal removes any underfill residue and excess solder on the substrate.  This part of the process must be done with extreme care in order to not damage the pads and adjacent components on the substrate. The site is then cleaned prior to inspection. Once cleanup of the substrate is complete, a new chip can be aligned, reflowed, and underfilled.

Call BEST (847-797-9250) today to see how we can assist you on reworking your underfilled devices. 

 

Underfilled Flip Chip Prior to ReworkUnderfilled Flip Chip Prior to ReworkSite cleaned and Ready for Device ReplacementSite cleaned and Ready for Device Replacement

BGA Rework Processes

rework-processBGA / LGA Rework Processes The following describes the general BGA rework process covering the development and criteria for establishing profiles for BGA removal and replacement. The materials required for such an operation are outlined below. Critical elements of the BGA / LGA rework operation including paste pattern printing and rework profile development are described in great detail in this BGA rework process outline. There are several technologies which can be used as the heat source in removal of a BGA including but not limited to hot air and IR. The BGA rework process described herein is generic in nature to the type of heating system used. The experience BEST has gained in reworking thousands of BGAs on hundreds of different customer PCBs has shaped the information found in this process description. BEST has expertise on stacked package (PoP) rework as well.

Material Required
  • Solder paste flux
  • BGA and LGA Rework System including computer-controlled heating source on the part area, PCB preheater capable of heating underneath entire board area, calibrated vision system, automatic vacuum pick up system and data logging functionality
  • XRAY System
  • Endoscope or other optical inspection system
  • Squeegee
  • Stencil
  • Kapton Tape
  • Hand held soldering system
  • Reflow oven
  • Solder wick or solder extraction tool
  • Stereo microscope

The BGA rework process can be methodically worked out by following these process guidelines though difference in printed circuit boards, devices populated on those boards. Years of experience, the correct equipment and a robust BGA rework process all help to insure high expected yields.  Whileseveral skills can be trained including but not limited to BGA rework profiling, site preparation and process troubleshooting, having the “real world” experience of hundreds of different boards and part configurations make this a skill which is supported by experiences. By having the right equipment the BGA rework process will go much easier. For example some of the packages and board combinations are better-suited for hot air rework systems while other combinations are better-suited for infrared rework heat sources. Hot air non-contact excavation source are better-suited for sensitive boards susceptible to lifter pads or damages solder mask while robust printed circuit boards can have the solder wicking approach for site preparation be more appropriate and cost-effective for the BGA rework process.

 

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Newsletter

WHAT'S NEW?

ARTICLE: Multiple Methods for Applying Paste Flux or Solder Paste for BGA Rework

ARTICLE: IPC-A-620 Gets a Facelift

 

 

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